In an electrophotographic printer, a photo-conductive drum or surface is exposed to illumination, generally by laser, to form a latent image on the drum surface. Toner is then applied to the latent image to develop the image. The developed image is transferred onto a print media and moved to a fixing device where the transferred image is fixed rather permanently to the media. For electrophotographic systems that print on rather uniform print media, it is relatively easy to maintain synchronization between the photo-conductive drum and the print media to place the image with precision on the desired area of the media.
However, when an electrophotographic printer is called upon to handle kinds of print media, having different thicknesses or made of different compositions, it is not unusual for the photoelectric drum to lose synchronization slightly with the movement of the print media. Additionally, the print media can have a different humidity; there may be variations in the diameter of the fixing rolls, there may be changes in the thickness of the media at the fixing rolls; all causing the print media to move out of phase with the associated area of the circumferential peripheral surface of the photo-conductive drum.
Such a problem becomes exceedingly serious with respect to processing of continuous form print media in which the misregistration or justification errors are accumulated along the length of the continuous form.
This problem has been recognized, and one proposed solution is the subject of the Negishi et al. U.S. Pat. No. 4,870,434 granted Sep. 26, 1989.
The Negishi et al. patent describes a possible solution in which the speed of the print media is monitored to determine the lapse time of media movement and to determine the number of scan lines placed upon the photoelectric conductor drum during the elapsed time required to move a selected segment of the print media. If the desired number of scan lines are not placed on the photo conductive drum during the elapsed time, then the scanning is interrupted or delayed to accommodate for the variance. In the specific implementation, the delay is caused to occur between the third and fourth line of textual material to increase or decrease the white line spacing therebetween. Such a system requires a complex delay circuit system for delaying the image information scan lines.
One of the objectives of this invention is to provide an improved solution for overcoming such variances which are more adaptable to a wide variety of different kinds of print media having different widths, having different compositions and having varying thicknesses. These and other objects and advantages will become apparent upon reading the following detailed description of a preferred embodiment.